1. Field of the Invention
The invention relates to a method for heating a glow plug for a diesel engine to a desired or set temperature, by passing current through the glow plug in a controlled manner.
2. Description of Related Art
A method of the above noted type is used to bring a glow plug of a diesel engine up to the set temperature at which the engine can be started.
A method for controlling the heating-up of a glow plug for a diesel engine is known from MTZ 10/2000 “The electronically controlled ISS glow system for diesel engines”, in which the glow command or the glow request is given after initialization of the engine control system has been completed, after the temperature of the engine elements has been determined via the engine control system and communication has then been successfully set up between the engine control system and the glow controller.
In order to control the heating-up of a glow plug of a diesel engine, it is important to know the thermal state of the glow plug, especially in the case of a quick-start glow plug, for example, the residual temperature of the glow plug after a previous glow process during a re-start, and to incorporate it in the subsequent control.
A quick-start glow plug which is designed so that its nominal voltage lies far below the available supply voltage in order to achieve a short heat-up time and which, for example, is designed for a voltage of 5 V in order to achieve an inertia temperature of 1000° C. at a supply voltage of 12 V, has hitherto been operated such that the resistance of the glow plug is checked before initiating the quick-glow phase in order to determine any glow process which may have taken place previously. If an already hot glow plug is heated, it can be damaged by excess temperature. Thus, for safety reasons, if a hot glow plug is identified, for example, in the event of a re-start, this is only acted upon with a low voltage, e.g., the nominal voltage, in order to avoid any overheating. However, this has the disadvantage that this following glow process takes place very slowly so that the glow plug requires a very long time to reach the desired temperature. For example, if the ignition key is actuated twice in quick succession, the pre-glow phase of the second pre-glow process requires about 10 seconds as compared with a value of 2 seconds in the first glow attempt in order to reach the same temperature.